1. Field of the Invention
The present invention relates to a pseudo noise generator employed to generate pseudo noise, etc., for evaluating the immunity of electric devices to electro-magnetic interference waves.
2. Description of the Prior Art
When many kinds of electrical or thermal or city noise combine with one another, the amplitude of the noise has a Gaussian distribution. In order to make generated noises simulate the Gaussian distribution, there has been proposed a noise generator for generating white-Gaussian noise by the use of a noise diode.
In narrow-band digital communication systems, there is a correlation between a bit error rate of the narrow-band digital communication system and an Amplitude Probability Distribution (referred to as the xe2x80x9cAPDxe2x80x9d) of the electro-magnetic interference waves. Moreover, a report was published that the bit error rate of a communication system can be evaluated from the APD of the electro-magnetic interference waves. In this report, noise determined by a specified APD is generated by the use of an arbitrary distribution random number generator (Paper Journal of the Institute of Electrical Communication Engineers of Japan (A), vol. J 70-A, No. 11, pp. 1681-1690, Nov. 1987).
Important parameters for defining the characteristic nature of noise are the APD, a Crossing Rate Distribution (referred to as a CRD), a Pulse Duration Distribution (referred to as a PDD), and a Pulse Spacing Distribution (referred to as a PSD), etc. These parameters will now be described with reference to FIG. 13.
The APD is defined as a time rate where the instantaneous value of a signal, such as electro-magnetic interference waves, exceeds a predetermined value, to show a total time length of the instantaneous value exceeding a level Ek in a test time period T0. The CRD is defined as the number of crossing per unit time where to instantaneous value of the signal crosses the specified level Ek in a positive direction (or a negative direction).
The PDD is defined as a probability distribution of the time Wi(k) where the instantaneous value of the signal exceeds a level EK in a test time period of T0. In contrast, the PSD is defined as a probability distribution of a time Zj(k) where the instantaneous value of the signal lowers a level EK in a test time period of T0. In other words, the PDD and the PSD are probability distributions of time lengths from a time where the instantaneous value of the signal crosses the threshold value to a just succeeding time where the instantaneous value of the signal crosses the threshold value.
Moreover, a Probability Density Function is defined as a distribution of the level EK in the test time period T0.
In a pseudo noise generator, the dispersion and the average of noise can be specified, but the APD of noise cannot be specified since the distribution of noise is limited to white-Gaussian noise.
In an arbitrary distribution random generator, the APD of noise is specified to generate noise with an arbitrary APD. However, noise from the arbitrary distribution random generator assumes independent events having no time-correlation. On the contrary, noise from electronic ranges and ordinary electronic devices assumes non-independent events dependent on the period of a source voltage and the period of timing clock pulses. Accordingly, the CRD, the PDD and the PSD of noise from the arbitrary distribution random generator are different from the CRD, the PDD and the PSD of noise of non-independent events having time-correlation.
An object of the present invention is to provide a pseudo noise, generator capable of specifying and Pulse Duration Distribution and a Pulse Spacing Distribution of noise at a specified amplitude level K in addition to an Amplitude Probability Distribution of noise.
To this end, a pseudo noise generator of the present invention comprises:
a first arbitrary random number generator for generating two groups of first random number signals respectively corresponding to, pre-divided Amplitude Probability Distributions, which are obtained by pre-dividing a specified Amplitude Probability Distributions into two parts at a specified level:
a second arbitrary random number generator for generating two groups of second random number signals respectively defined by a specified Pulse Duration Distribution and a specified Pulse Spacing Distribution at the specified level;
control means for selecting one of said two groups of first random number signals in accordance with said specified Pulse Duration Distribution and said specified Pulse Spacing Distribution and said specified Pulse Spacing Distribution at the specified level.